The present invention relates to an airflow indicator. More particularly, it relates to an airflow indicator that signals when a filter chamber in a vacuum cleaner is full.
Typical vacuum cleaners load a suction motor more and more as a dirt holding means such as a dirt bag, cup, container or the like becomes full. Many vacuum systems use the airflow through the system to cool the motor (particularly in clean air type vacuums). As the dirt holding means of the vacuum becomes more and more full, there is less and less cooling air passing through the motor. The end result can be a reduced motor life due to increased loading.
One attempt at remedying this problem is the use of a hold-open thermostat device which shuts the unit off when the system airflow is not adequate to cool the motor. The hold-open thermostat device then prevents the motor from driving a brush roll of the vacuum cleaner until the motor has cooled down, such as for a period of thirty minutes or more.
There are several reasons that the hold-open thermostat is not a good solution. Once the unit heats up to the trigger point, the consumer can no longer finish cleaning the carpet/surface. The fact that the unit will shut off and remain off for a period of thirty minutes or more is a big inconvenience to the consumer and therefore a product return issue as well.
Other vacuum systems have employed a bleed valve that opens an additional air path to the motor once the airflow through the motor is reduced to a certain level. The reduced (specified) level of airflow corresponds to a vacuum pressure value located at the bleed valve location. After some testing, a pressure value for the desired opening pressure is determined. Using this pressure value, a spring-loaded valve can be designed to open once the pressure reaches the target value.
Currently, many vacuum bleed valve systems use a spring-loaded valve employing a wire form spring. The wire form spring is part of an assembly which has a plunger that usually floats on the top end of the spring. The plunger also interfaces with another surface and commonly creates a seal based on the force of the compressed wire form spring.
Other vacuum manufacturers use valves to indicate airflow to the consumer. Often this is done by displacement of a part once a certain pressure is achieved. For example, some vacuums have used a pin which displaces with the valve head once the open pressure is achieved to indicate that the final filter (often now a HEPA filter) may need replacement on the vacuum.
Although it is not exactly a valve, some vacuum manufacturers use a full bag indicator having a plunger that moves in front of a clear window where it can be observed by the consumer. A change in position of the plunger is due to a pressure difference. The travel of the plunger is due to a small air hole which allows the plunger to move in the direction of the airflow. Since the airflow is so small, the plunger arguably operates on a static pressure difference.
One problem with air valve springs is that they often have low spring rates and large displacements once the desired opening pressure is reached. Larger spring rates are not feasible because a large spring rate usually translates to a system that is too sensitive to variations in assembly and manufacturing methods. With low spring rates, there are many inherent difficulties in achieving a system that performs accurately and precisely. In particular, the wire form spring design approach has many challenges. Often times, variations in plastic part dimensions prevent consistent compression. Variations in the wire form manufacture are costly to minimize and often require the use of precision springs. Even then, the variations expected with regard to the performance of an air valve are large. Often times, the displacement of the valve is different from valve to valve, and this results in different airflow rates into the bleed valve. In fact, many air valve manufacturers have to inspect one hundred percent of all the assemblies they ship.
Another problem with the prior art systems described above is that once the air valve opens, it is often difficult to have the valve close at a desired pressure that is different than the opening value and ideal for customer use. The bleed valve will open under the sealed suction condition, and this often occurs intermittently when the consumer is cleaning furniture or using hand tools with the vacuum. It is desirable to have the valve close back up unless the filter needs cleaning. It is very difficult to try to control the close value of a valve system that uses a wire form spring. Sometimes the valve will remain open due to the airflow through the valve. Finally, friction is always a factor in a system that relies on surface-to-surface travel or displacement.
Accordingly, it has been considered desirable to develop a new and improved airflow indicator which would overcome the foregoing difficulties and others while producing better and more advantageous overall results.